Now that I've gotten a feel for the general differences between the procrastinated and non-procrastinated papers I collected, I'm going back over the procrastinated ones to better understand what's going on there. Here's what I've learned about "Mark"'s paper.
Mark reports that he wrote his research paper two days before it was due and then rewrote the whole thing one day before it was due. He says he put it off so long because he's "lazy," but he feels he spent enough time on it anyway.
He's right at the average length for the papers in his class and has rate of surface errors in the first quartile. And his sentence structure seems reasonable for a FYC class with pretty frequent subordination. So his lack of error isn't obviously caused by avoiding challenges. He didn't report doing any proofreading.
On the other hand, his rate of problems with evidence is the highest in his class. His top two problems are weak lead-ins for quotations and unsupported claims. (These are the top two problems for non-procrastinators in his class as well.) In Mark's case, most of his quotations are "dropped in" without signal phrases, but they do logically follow the sentences before them. He also relies completely on secondary sources about a comic book character, never directly citing the comics themselves.
It's hard to say whether starting his paper a few days sooner would have helped Mark. It might have given him more time to look up sources for some of the claims he wanted to make. But it probably wouldn't have prevented his dropped quotes. In my experience teaching and tutoring, people who drop quotes simply don't understand that it's a no-no--even after multiple one-on-one sessions intending to explain it. Unless he used those extra days to take his paper to the writing center or conference with his instructor, Mark probably wouldn't have fixed those dropped quotes because he probably didn't think they needed fixing.